1. Field of the Invention
The present invention relates to a vehicle comprising a driveshaft transmission system, comprising a driveshaft and a hub at a wheel of said vehicle, where said vehicle further comprises a battery pack and an electric motor for propelling said vehicle, said electric motor being arranged at said driveshaft. The invention further relates to a method for controlling a vehicle comprising a driveshaft transmission system and an electric motor.
2. Description of Related Art
It is commonly known to arrange a driveshaft on a bicycle instead of a more common and cheap drive chain connecting a front sprocket at the crank to a rear sprocket at the hub on the rear wheel. Using a drive shaft solution provides a number of advantages, one very important advantage being that the solution is more or less maintenance-free. Another advantage of the driveshaft transmission is that it provides a very simple and sophisticated solution that can easily be combined with a smart design, and of course that the use of trouser clips or chain guard is no longer necessary as the movable and greasy parts are hidden inside the driveshaft construction.
Further it is also commonly known to arrange an electric auxiliary motor on a bicycle to assist the user while pedalling. In the various countries there are different rules and laws stating how such an auxiliary motor may be operated, but it is very common that the user of the bicycle needs to be pedalling—to apply some torque on the crank—to allow the electric auxiliary motor to assist.
Over the last years it has become more and more popular to ride such bicycles with an electric auxiliary motor, but still there is a strong desire to have a bicycle with an stylish and simple design, which is very often not the case with bicycles with electric auxiliary motors placed in the crank area as they tend to appear rather clumsy as the auxiliary motor are quite big.
Japanese Patent Application JP 5058379 A by Yamaha Motor Co. Ltd. discloses a bicycle having a driveshaft transmission and where an electric auxiliary motor of the internal rotor type is built into the crank of the bicycle. As the electric motor is arranged in the crank it needs to transmit its power to the crank shaft running at a relatively low rpm. This is a very demanding task as it is commonly known that electric motors running with a low number of revolutions will only be able to transfer a very low torque.
From Japanese Patent Application JP 2001213381 by Honda Motor Co. Ltd., another bicycle with electric auxiliary motor of the internal rotor type and a driveshaft construction is known. In this solution, the auxiliary power can come from one or two electric motors arranged directly at the shaft. In order to let the shaft run with a higher number of revolutions, a rather large gear transmission is arranged in the crank and the electric motor has a rather small diameter which, as in the Yamaha document, leaves the bicycle with a ineffective auxiliary motor that cannot provide the torque required to propel or at least assist the person using the bicycle in a proper manner. Also, in this Honda document the crank is rather complex and clumsy as the mentioned large gear need to be there and also a one-way clutch is installed inside the crank.
Both the mentioned bicycles with shaft transmission and with an electric auxiliary motor of the internal rotor type have a very special crank design and a rather inefficient use of the electric motor. In order to produce such bicycles, a rather complex design work has to be done as the complete transmission system is more or less special and different compared to a standard bicycle transmission system using a drive shaft.